Biochemical pathways of visual transduction in frog rod outer segments will be probed using monoclonal antibodies to photoreceptor proteins. (1) Using a number of antibodies to the G-protein already in hand, the functional effects of antibody binding to the G-protein will be characterized in disrupted outer segments by assaying GTP binding, cGMP phosphodiesterase activity, and protein phosphorylation. Antibodies that block G-protein function will be used to study biochemical interrelationships in the light-activated cGMP pathway. (2) Monoclonal antibodies will be generated to other rod outer segment proteins potentially important in visual transduction; e.g. cGMP phosphodiesterase, Components I and II, rhodopsin kinase, cGMP-dependent protein kinase, etc. These antibodies will also be screened for effects on protein function, and then used in studies on the roles of these proteins. (3) Depending on the progress of (1) and (2) G-protein antibodies will be used to probe the structure-function relationships of the G-protein, and its homologies with the G-protein important in many hormone responsive systems.